Virtual Labs

DSB-SC, SSB-SC Modulator & Detector

1. In a DSB-SC modulation scheme, assuming the message signal contains a wide range of frequency components, how would the sampling frequency requirement change if the message signal undergoes modulation, and how does the modulation scheme affect the risk of aliasing, considering the Nyquist-Shannon theorem?

a: The minimum sampling frequency for the modulated signal must be at least twice the maximum frequency of the message signal, as the modulation does not alter the frequency content significantly. Explanation

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b: The minimum sampling frequency should be at least twice the highest frequency of the modulated signal, which may involve a frequency range that exceeds twice the message signal’s highest frequency due to the modulation scheme's bandwidth expansion. Explanation

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c: Sampling at the Nyquist rate of the message signal is sufficient, as the modulation will inherently prevent aliasing by shifting the signal’s frequency spectrum. Explanation

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d: The sampling frequency must be much higher than twice the message signal’s frequency due to the frequency doubling effect of DSB-SC modulation, but aliasing can still occur if the signal is not band-limited before sampling. Explanation

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2. How does the phase shift of the local oscillator affect the demodulation of an SSB-SC signal?

a: The phase shift must match exactly the phase shift of the original modulating signal for optimal demodulation. Explanation

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b: The phase shift of the local oscillator does not affect the demodulation of an SSB-SC signal. Explanation

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c: The phase shift of the local oscillator enhances the signal-to-noise ratio of the demodulated output. Explanation

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d: An incorrect phase shift can result in significant distortion or loss of the message signal. Explanation

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3. What is the impact of a non-ideal filter on the recovered message signal in an SSB-SC system?

a: Non-ideal filtering reduces the overall signal power but preserves the message signal shape. Explanation

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b: Non-ideal filtering enhances the signal-to-noise ratio by removing unwanted frequencies. Explanation

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c: Non-ideal filtering can introduce distortions such as frequency distortions or amplitude variations. Explanation

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d: Non-ideal filtering does not affect the message signal if the filter's cutoff is set properly. Explanation

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4. In a DSB-SC system, what is the effect of phase mismatch between the transmitted and received carrier signals during demodulation?

a: Phase mismatch only affects the frequency of the output signal without altering its amplitude. Explanation

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b: Phase mismatch results in a reduction of the output signal amplitude and introduces significant distortion. Explanation

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c: Phase mismatch does not affect the demodulation process if the amplitude of the received signal is sufficient. Explanation

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d: Phase mismatch results in an increase in the overall signal power. Explanation

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5. How does the use of a balanced modulator impact the performance of a DSB-SC system?

a: A balanced modulator increases the power of the carrier signal in the output. Explanation

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b: A balanced modulator helps suppress the carrier and reduces unwanted spurious signals. Explanation

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c: A balanced modulator simplifies the receiver design by eliminating the need for coherent detection. Explanation

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d: A balanced modulator has no significant impact on the performance of the DSB-SC system. Explanation

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6. In an SSB-SC system, what are the primary challenges faced in achieving perfect carrier suppression?

a: Challenges are mainly related to the bandwidth of the message signal. Explanation

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b: Challenges involve the use of non-linear amplifiers in the transmission chain. Explanation

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c: Challenges are associated with the power of the transmitted signal. Explanation

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d: Challenges include maintaining precise oscillator frequency and phase synchronization, and handling non-ideal components. Explanation

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7. In DSB-SC modulation, what role does the Hilbert transform play in the signal processing chain?

a: The Hilbert transform is used to create the analytic signal, which is crucial for generating the modulated signal. Explanation

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b: The Hilbert transform adjusts the amplitude of the signal to fit the desired modulation index. Explanation

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c: The Hilbert transform is used to filter out the carrier frequency from the modulated signal. Explanation

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d: The Hilbert transform is used to demodulate the DSB-SC signal directly. Explanation

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8. For an SSB-SC signal, how can the presence of noise impact the phase detection process during demodulation?

a: Noise improves phase detection by spreading the signal's frequency components. Explanation

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b: Noise will only affect the amplitude of the received signal, not the phase detection. Explanation

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c: Noise can cause phase jitter, leading to incorrect phase detection and loss of signal fidelity. Explanation

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d: Noise does not affect the phase detection if the signal-to-noise ratio is high. Explanation

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9. What is the primary function of a synchronous detector in the reception of DSB-SC signals?

a: A synchronous detector synchronizes the received signal's carrier phase with the local oscillator, enabling coherent demodulation of the message signal. Explanation

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b: A synchronous detector eliminates the need for a local oscillator by directly extracting the message signal from the carrier. Explanation

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c: A synchronous detector filters out both in-band and out-of-band noise to improve the quality of the demodulated signal. Explanation

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d: A synchronous detector amplifies the received signal and compensates for any amplitude variations before demodulation. Explanation

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10. In SSB-SC modulation, what is the primary reason for implementing a phase-locked loop (PLL) in the demodulation process?

a: A PLL enhances the amplitude of the received SSB-SC signal for better visibility. Explanation

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b: A PLL is used to lock onto the carrier frequency and phase, ensuring accurate demodulation of the SSB-SC signal. Explanation

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c: A PLL eliminates the need for a coherent detector in the demodulation process. Explanation

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d: A PLL reduces the bandwidth of the demodulated signal to fit within system constraints. Explanation

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